import java.util.Scanner;

public class Demo1 {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int w = scan.nextInt();
        int h = scan.nextInt();

        int[][] array = new int[w][h];
        int count = 0;

        for(int i=0;i < w;i++) {
            for(int j =0;j < h;j++) {
                if(array[i][j] == 0) {
                    count++;

                    if(i+2 < w) {
                        array[i+2][j] = 1;
                    }

                    if(j+2 < h) {
                        array[i][j+2] = 1;
                    }
                }
            }
        }

        System.out.println(count);
    }
}
